Patch array antennas are among conventional array antenna devices having a microstrip structure which are used for wireless communication or wireless positioning. FIG. 19(A) is a plan view showing the configuration of a conventional patch array antenna in which four patch elements 502a, 502b, 502c, and 502d and a feeding circuit are arranged on one surface of a dielectric substrate 501. FIG. 19(B) is a sectional view of the dielectric substrate 501.
In the patch array antenna shown in FIGS. 19(A) and 19(B), the patch elements 502a, 502b, 502c, and 502d are arranged as radiation elements on the one surface of the dielectric substrate 501 and a ground conductor 503 is formed on the other surface of the dielectric substrate 501. The patch elements 502a, 502b, 502c, and 502d are fed with power via a branching circuit 504 which consists of microstrip lines. Being thin in structure, the patch array antenna shown in FIGS. 19(A) and 19(B) can realize a high-gain radiation characteristic.
The loop-line antenna described in Non-patent document 1 is known as a conventional array antenna device. FIG. 20 is a perspective view showing the configuration of a loop-line array antenna as a conventional array antenna device. Where a microstrip line 602 is formed on a dielectric substrate 601, the loop-line array antenna shown in FIG. 20 includes radiation cells 603a, 603b, 603c, 603d, 603e, 603f, 603g, and 603h as loop-shaped radiation elements formed at regular distances.
The circumferential length of each of the radiation cells 603a, 603b, 603c, 603d, 603e, 603f, 603g, and 603h is approximately equal to one wavelength of radiated radio waves, and the distance between adjoining radiation cells is also approximately equal to one wavelength of radiated radio waves. Being simple in the feeding structure, the loop-line array antenna shown in FIG. 20 can be reduced in the number of radiation cells and radiate good circularly polarized waves.